Hollow fiber filter for extracorporeal blood circuit

ABSTRACT

A filter for an extracorporeal blood circuit including: a bundle of hollow fibers having an end section encased in a potting material, wherein the end section further comprises a stem of fibers and potting material and an annular disk of the potting material extending radially outward from the stem, wherein the annular disk of the potting material is substantially wider than the stem, the stem protrudes from the disk and the stem includes a side surface extending along a length of the stem; an end surface of the stem substantially perpendicular to the length of the stem and including open ends of the fibers distributed throughout the end surface including open ends proximate to a perimeter of the end surface; a filter housing through which extends the bundle, the filter housing comprising a tubular section and a first end section and a second end section at opposite ends of the tubular section, wherein the annular disk is seated in the first end section and the stem is narrower than the tubular section along the length of the stem; a filter header cap mounted on the first end section of the filter housing, wherein the filter header cap includes an inlet connectable to a blood line and an open end, the filter header cap including a cap side surface abutting the stem side surface, and the second end section connectable to a blood line.

RELATED APPLICATION

This application is a continuation of the application for U.S. Pat. No.7,297,270 (U.S. application Ser. No. 10/748,135 filed Dec. 31, 2003),and claims priority to U.S. Provisional Application 60/459,967, filedApr. 4, 2003, the entirety of which applications are incorporated byreference.

FIELD OF INVENTION

This invention relates to a method and apparatus for a hollow fiberfilter used in the treatment of extracorporeal blood, such as in renalreplacement therapies. In particular, the invention relates to a headercap for a filter header housing a bundle of hollow fibers havingminimized blood residence time in the header, minimum blood contact withheader cap surfaces, and a smooth blood flow profile through the header.

BACKGROUND OF THE INVENTION

1. Renal Replacement and Fluid Overload Therapies

The term “Renal Replacement Therapy” (RRT) generally refers to all formsof dialysis, solute and fluid balancing therapy. Renal replacementtherapy performs two primary functions: ultrafiltration (removal ofwater from blood plasma), and solute clearance (removal of differentmolecular weight solid substances from blood plasma). The filter, alsocalled hemofilter or “dialyzer”, used in RRT may perform either or bothof these functions simultaneously, with or without fluid replacement.Various modes of renal replacement therapy relate to whether fluids,solutes or both are removed by the filter and whether fluids arereplaced into the filtered blood. “Clearance” describes the removal ofsubstances, both normal and waste products, from the blood whether bynormal kidney function or during renal replacement therapy.

Fluid overload therapy relates to removal of excess fluids fromextracorporeal blood in patients that, for example, suffer fromcongestive heart failure (CHF). Patients suffering from CHF haveweakened hearts that are unable to provide normal blood flow to thekidney and organs of the body. CHF patients may have normal kidneys, butlack sufficient blood flow to maintain proper kidney functions ofremoving excess fluid, e.g., water, from the body. The build-up ofexcessive fluids due to inadequate kidney functions further increasesthe blood pumping load on the heart, which is already suffering fromCHF.

Dialysis is the diffusive transfer of small solutes out of a bloodplasma compartment by diffusion across a membrane of a filter. Diffusionof the solutes occurs due to a concentration gradient across the filtermembrane. Diffusion occurs from the filter compartment with higherconcentration (typically the blood compartment) to the filtercompartment with lower concentration (typically the dialysatecompartment). Since the concentration of solutes in the plasmadecreases, clearance is obtained, but fluid may not be removed.Ultrafiltration can be combined with dialysis.

Hemofiltration is the combination of ultrafiltration and fluidreplacement, typically in much larger volumes than needed for fluidcontrol. The replacement fluid contains electrolytes, but not othersmall molecules. Since the net effect of replacing fluid without smallsolutes and ultrafiltration of fluid with small solutes results in netremoval of small solutes, clearance is obtained.

Ultrafiltration and hemofiltration operate primarily by convection ofsolutes through the filter membrane. In hemofiltration, a solutemolecule is swept through a filter membrane by a moving stream ofultrafiltrate. Proteins and blood cells are retained in the blood by themembrane. In patients with renal failure, renal replacement therapy,such as hemofiltration or dialysis, removes undesired solutes from theirblood. In renal replacement therapy, vital elements such as electrolytesare also removed from the blood and need to be replaced to maintainelectrolyte balance. Thus, hemofiltration and dialysis treatmentsusually require fluid replacement. In contrast, ultrafiltration does notremove substantial amounts of electrolytes and solutes.

Hemodialysis requires a large filter membrane surface to enableeffective solute clearance by diffusion. Hemofiltration requires largeamounts of ultrafiltrate to be transferred across the membrane to removea relatively small amount of solute. Large amounts of fluid such as 1 to4 liters per hour (L/hour) are continuously being removed duringcontinuous veno-venous hemofiltration (CVVH). The resulting loss ofwater and electrolytes are immediately dangerous to the patient. Tomaintain fluid and electrolyte balance, an equally large or slightlylower amount of replacement fluid is infused into the patient.Replacement fluid is thus added into the extracorporeal blood circuitbefore or after the filter.

Ultrafiltration utilizes extracorporeal blood filters to remove fluidsfrom blood, where the filter generally includes a blood passage havinginput and output ports, a filtered fluid discharge port and a finelyporous membrane separating the blood passage and the ultrafiltrate offiltrate discharge port. The ultrafiltrate output from the filter issubstantially all fluids, e.g., water, and is relatively free ofsolutes.

Different modalities of Continuous Renal Replacement Therapy (CRRT) havebeen used to treat patients suffering from excess fluid overload andacute renal failure. In the acute condition, CRRT has been performedusing standard methods of hemodialysis and continuous arterio-venoushemofiltration (CAVH). More recently, CVVH has been used to reduce thecomplications associated with such issues as hemodynamic instability andneed for arterial access.

2. Limitations of Existing Blood Devices

Extracorporeal blood treatment usually requires anticoagulation of bloodto avoid blood clots forming the in blood circuit. Blood coagulation istypically activated by shear and by the contact of blood to theartificial surface of the extracorporeal circuit. Blood does not clotuntil several minutes after the activation of the clotting system.Reducing the residence time of blood in a blood circuit can allow theblood to flow through the circuit and back into the blood stream of thepatient before a clot forms. Once the blood is returned to the naturalcirculatory system of the patient, the blood clotting activation processstops. Accordingly, delays in the movement of blood through theextracorporeal blood circuit may allow the clotting activation processsufficient time within which to form a clot.

FIGS. 10, 11, 12 and 13 are enlarged cross-sectional views ofconventional filter headers 511, 512 and 513 such as sold under thetrade names Gambro FH22H™, Cobe M60™ and Fresenius F80™. The filterheader cap 512 (See, e.g., U.S. Pat. No. 4,990,251) has a separatepolymer seal ring 532 forming a face seal between the rim 531 of thepotting compound and the filter header cap 533. The rim is an annularring of potting compound that is devoid of hollow fiber filters and isimpervious to blood. Blood that flows to the gap between the rim 531 andcap 533 eddies just inside the circumference of the seal ring 532 andtends to clot at the seal ring. A conventional filter header cap 511such as the Cobe M60™ has a sealing tooth 530 instead of the sealingring of the header cap 512.

Sealing rings and teeth are not employed in some conventional filterheaders 513, e.g., the Gambro FH22H™. The filter header cap 513 has afilter header cap 535 that is welded or bonded to the outer perimeter ofthe cylindrical filter case 536. As is shown in FIG. 11, which is anenlargement of the region 11 in FIG. 10, a wide annular dead zone 538exists between the cap and the rim formed by the end of the filter case536 and the rim of impervious potting compound 537. Blood clots tend toform in dead zones. The conventional filter headers shown in FIGS. 10 to13 each have significant dead zone areas 538, which typically have awidth of 2.54 mm to 5.08 mm (0.10 to 0.20 inches). These dead zonesresult in the stagnation of blood and promote the formation of bloodclots.

FIG. 14 is a graph of simulated streamlines of the blood flow through aconventional filter header cap have a wide dead zone 538. Thestreamlines were generated by Computational Fluid Dynamics that predictthe flow streamlines within various filter cap flow paths. Smooth streamlines of blood 540 show the blood passing through the filter header capand into the open hollow fibers of the filter. Smooth stream linessuggest the absence of dead zones, flow eddies and recirculation.However, the dead zones 538 at the potting compound rims result inrecirculation areas 541 (FIG. 14) of the blood flow.

Delays in the blood circuit occur if the fluid path contains poorlyperfused dead zones where blood stagnates for a long period, such as ineddy pools and at flow blockages that force the blood to recirculatethrough a portion of the passage. A common location for dead zones is inthe entrance header cap of a filter, where the blood flows from narrowblood tubes towards the relatively wide entrance of a fiber bundle. Thefiber bundles are typically encircled by annular rims of pottingcompound. These impervious rims are at the outer periphery of the headercap and at the side-wall of the filter housing. These rims form deadzones in the blood flow. The rims block the flow of blood and cause theblood to stagnate and recirculate in eddy currents in the filter headercap. Blood clots tend to form in the dead zones. The clots eventuallywill block the filter and entire circuit.

SUMMARY OF THE INVENTION

A hollow fiber filter has been developed that has a filter header withan optimized streamlined blood passage that is substantially free ofobstructions and dead zones.

In a first embodiment the invention is a filter for an extracorporealblood circuit comprising: a bundle of hollow fibers having an endsection encased in a potting material, wherein said end section ofpotting material has an end surface with open ends of the fibersdistributed throughout the end surface, and a filter header having aninlet connectable to a blood line and an open end sealed around a sidesurface of the end section of the bundle of hollow fibers.

In a second embodiment the invention is a filter for an extracorporealblood circuit comprising: a bundle of hollow fibers having an endsection encased in a potting material, wherein said end section has astem of fibers and potting material upstanding from a disk of thepotting material and the stem has an end surface with open ends of thefibers distributed throughout the end surface including open endsproximate to a perimeter of the end surface, a housing through whichextends said bundle; a filter cap at an end of said housing, wherein thedisk of the potting material is sealed to the cap, and a filter headerhaving an inlet connectable to a blood line and an open end sealedaround a side surface of the stem.

SUMMARY OF THE DRAWINGS

A preferred embodiment of the invention and limitations of currentdesigns are illustrated in the attached drawings.

FIG. 1 illustrates an embodiment of an extracorporeal circuit having ablood filter.

FIG. 2 is side view of a filter with a filter header separately shown atone end of the filter.

FIG. 3 is an end view of the filter.

FIG. 4 is a cross-sectional view of the filter taken along line 4-4 ofFIG. 3.

FIGS. 5 and 6 are enlarged cross-sectional views of a portion of thefilter near the filter header. FIG. 6 is an enlargement of region 6marked in FIG. 5.

FIG. 7 is an end view of the filter.

FIG. 8 is an enlarged end view of the filter showing the region 8 ofFIG. 7.

FIG. 9 is a side view of the filter header portion of the filter showinga simulation of blood flow stream lines through the header.

FIGS. 10, 11, 12, and 13 are each cross-sectional side views ofconventional filter headers of prior art filters.

FIG. 14 is a side view of a conventional filter header showingsimulations of blood flow stream lines through the header.

FIGS. 15 and 16 are each side views of proposed filter header designsshowing simulations of blood flow stream lines through the headers.

DETAILED DESCRIPTION OF THE INVENTION

The outer periphery of the end of the fiber bundle extends to or nearthe side-wall of the filter housing. Blood at the sidewall of the filterheader may flow into the open ends of fibers that are positioned next tothat sidewall. Thus, a dead zone does not form next to the sidewall ofthe filter header. The disclosed fiber bundle minimizes dead zone byminimizing the solid potting compound rim that is at the outer edge ofthe potted filter area. The interior geometry of the filter headerreduces dead zones at the entrance to the bundle of hollow fibers in thefilter and thereby minimizes flow eddies and recirculation zones in theblood path of the header. The blood flow transitions from a bloodconduit tube having a 3.2 mm internal diameter to a stem of the fiberbundle having a diameter of 11.43 mm at its end surface 505. Thus, thestem diameter is only about 3.6 times (and less than four times) thetube internal diameter. The transition in the header from the smalldiameter tube to the large diameter fiber bundle is prone to floweddies, and blood recirculation that creates dead zones. The filterheader minimizes blood flow eddies and recirculation dead zones by anovel filter header geometry and height between the potted filter bundleand header inlet port to streamline the blood flow through the header.

FIG. 1 illustrates an extracorporeal circuit having a filter 207 toremove fluid from extracorporeal blood. The fluid path includes adisposable extracorporeal circuit 202 for a treatment device coupled toa console having a peristaltic blood pump, and a pump display and amicroprocessor control unit. Blood is withdrawn from the patient throughthe withdrawal needle assembly 201. Blood flow is controlled by a rollerpump 204. The withdrawal needle assembly is connected to the bloodtubing 220 by a pair of matching connectors 230, 232. One connector 230is part of the withdrawal needle assembly and the mating connector 232is a part of the blood tubing 220. These connectors can either be anintegral part of the connected blood tubing or separate parts glued,welded or mechanically fixated with the tubing.

Blood tubing 220 is typically 2 m (meters) long and is connected to adisposable pressure sensor 203. The opposite end of the pressure sensor203 is further connected to blood pump tubing 221 that is connected to adisposable pressure sensor 205. Pressure sensor 205 is connected toblood tubing 222 leading to and permanently connected to the inlet ofthe blood side of the filter 207, e.g., a hemofilter. The outlet of theblood side of the hemofilter is connected to blood tubing 223 that isconnected to one side of a disposable pressure sensor 209. The otherside of the disposable pressure sensor 209 is connected to the bloodtubing 224 that ends with the connector 233. Connector 231 is part ofthe blood return needle assembly 210.

A filtrate line 212 is connected to the filtrate outlet 211 of thefilter 207 on one side and to the filtrate collection bag 215 on theother side. An ultrasonic air detector 206 is in contact with the outersurface of the blood tubing 222 and blood leak detector 213 is incontact with the outer surface of the filtrate tube. Both detectors 206,213 do not interrupt the smooth flow paths through the interiors of thetubes.

The filter 207 provides a smooth flow path for the blood through thefilter passages. The hollow fiber bundle provides a fiber membranesurface area of 0.1 m², which provides sufficient fluid removal duringoperation of the extracorporeal circuit. The long and thin bundle 501(FIG. 4) of hollow fiber filters promote a smooth flow path through thefilter. The fiber filter bundle 501 may have an effective length of 22.5cm and a fiber bundle diameter of 1.2 cm.

FIGS. 2 through 5 show the filter 207 comprising a hollow cylindricaltube 503 with end caps 560 at opposite ends of the tube. A long hollowfiber bundle 501 extends the length of the tube. A potting compound 502seals the ends of the fiber bundle in the end caps 560. Filter headercaps 504 slide over the ends of the filter stem 564 and couple the fiberbundles 501 to the tubing of the blood lines 222, 223. Blood enters thefilter 207 through a header cap 504 which directs the blood into theopen ends 580 of the fibers 501 at the filter cut surface 505. The cutsurface 505 has the open ends of fiber 501 each surrounded by pottingcompound 502.

The potting compound provides a mount for the fiber bundle 501 in thefilter and prevents blood from traveling around the fiber ends and intothe ultrafiltrate compartment 506. The potting compound may be amoldable resin that, when in liquid form, is cast around sections of thefiber bundle at opposite ends of the bundle. The end sections of thefibers are encased in the liquid resin compound. The resin is formed byan annular mold that allows the liquid resin to cure into a disk 562,through which extends the fiber bundle 501. A potted stem 564 of thefiber bundle extends axially outward of the disk 562. Fibers denselypopulate the entire cross-sectional area of the stem 564, including to arim proximate the outer perimeter of the stem. After the resin hashardened, the stem is cut to form an end surface 505 of open, hollowfiber ends and resin. The stem 564 is not cut flush with the face 563 ofthe disk 562, but rather extends axially outward of the disk. Theperimeter of the resin disk 562 is seated in the open cylindrical end ofthe of the filter cap 560. The seal between the resin disk 562 and thecap 560 is removed from the blood flow. The filter header cap has alarge diameter end 572 that fits over and seals with the end of the cap560. Adhesive may be applied to the secure the header end 572 to thefilter cap 560.

A narrow rim 514 (FIG. 8) of potting compound (without associated fiberends) surrounding the ends of the fiber bundle (to the extent such a rimeven exists) has a minimal thickness along the stem 564 of the ends ofthe fiber bundle. The rim 514 of the potting compound forms a thinannulus around the periphery of the blood contacting end surface 505 ofthe stem 564. The blood contacting end surface 505 of the stem ispopulated with open fiber ends to allow blood to flow through the entirearea of the end surface 505. For a filter with 900 fibers, each with anoutside diameter of 280 microns, the cut end surface 505 may have adiameter of 11.43 mm (0.45 inches) with a total surface area of 102.6mm². Of this total surface area, the exposed potting compound isdispersed among the fiber ends and the potting area is minimized to47.19 mm² (0.073 inches²), which is less than 50 percent of the totalsurface area. The width of outer rim 514 of potting compound (which isdevoid of fibers) is on average between 0.025 mm to 0.508 mm (0.001 to0.020 inches). It is believed that the amount of potting area in the endsurface 505 has been reduced by 70% as compared to the solid pottingcompound surface rim area of a conventional fiber design, such as isdisclosed in U.S. Pat. No. 4,990,251.

The filter header cap 504 has a conical shape that is preferably formedof a flexible plastic material, such as, 50 to 95 Shore A. The filterheader cap includes an small diameter cylindrical end 566 that connectsto a blood tube. The blood tube fits into a passage 568 in the end 566of the header cap that is coaxial with the header cap and filter. Thediameter of the passage steps-down at the end of the inserted bloodtube, so that the smaller diameter portion of the passage 568 has thesame diameter as the blood passage of the blood tube, 222,223.

The filter head includes a middle cylindrical section 569 having aninner surface 570 that seals around the outer surface cylindricalsurface 508 of the stem 564. The filter head material is soft andflexible to seal on the potted fiber bundle outer circumference 508 ofthe stem, without distorting, crushing, or occluding the filter fibersparticularly on the outside circumference of the cut surface 505. Theseal between the filter head middle section 569 and the stem 564 of thefibers is formed by an interference fit between the header cap 504 and astem 564 (formed of fibers and potting compound) of between 0.025 mm to1.27 mm (0.001 to 0.050 inches) depending on the actual cap diameter.The interference fit between the filter header cap and the potted fiberbundle establishes the height between the end surface 505 of the fiberbundle and the filter cap header cap 504. The interference fit causesthe filter header cap to seal to the circumference of the stem andthereby achieve the desired height between the end 505 of the fiberbundle and the inner surface 510 of the header cap. The header cap doesnot abut against the potting compound disk 562.

Additionally there may be a relief area 520, either in the cap or pottedsurface, to receive an adhesive that secures the filter header cap tothe stem. Other attachments may be used to secure the filter header caponto the stem and cap of the filter, such as thermal welding, screwthreads, or snap features.

The middle section 569 of the filter header cap forms an interiorchamber 574, 575 from the passage 568 to the stem end surface 505 withthe open ends of the fibers. The passage 568 may have a diameter 523that expands slightly, e.g., 5 degrees, as it opens to a corner 507having a radius of 30 to 70 percent of the inlet diameter 523. Theannular corner 507 opens to a center flow zone 575 and to an outerannular flow zone 574 between the inside surface of the header cap 504and the end surface 505 of the stem. The center zone 575 is aligned withthe open end of the aperture 568, and receives blood flowing in astraight stream from the aperture into fibers. The blood flow turnsradially outward from the diameter 523 around the corner 507 into theouter annular flow zone 574. The annular corner 507 and the annularinner surface 510 of the filter header cap are shaped to minimize floweddies as the blood flow turns the corner 507 and passes through theannular flow zone 574. The slope of the inner surface 510 of the headercap may curve smoothly to the outer rim 570 of the stem 564, where theinside surface 510 at its perimeter turns inward at an angle of 30 to 60degrees towards the stem. The depth 509 of the annular flow zone 574,which is between the end surface 505 of the stem and a tangent pointbetween radius 507 and contour 510 may be 0.381 mm to 1.016 mm (0.015 to0.040 inches). The depth 509 of the annular flow zone 574 is narrow toeliminate or minimize dead zones in that zone. The ratio of the depth509 to the diameter of the stem, e.g., 11.43 mm, may be less than 1(depth) to 10 (diameter of stem).

FIG. 15 shows recirculation stream lines 543 caused by an excessiveradius in the filter header cap 504. FIG. 16 shows recirculation streamlines 544 in a header caused by an excessive annular flow zone depth.

FIGS. 7 and 8 are end views of the filter 207, with the filter headercap removed. The cut end 505 of the stem 564 of the fiber bundle 501 isheavily populated with open fiber ends 580. These open ends receive theblood flowing through the header cap 504. The rim 514 of pottingcompound at the periphery of the stem is narrow and does not establish asubstantial dam to the flow of blood into the fibers.

FIG. 9 is a side view of a half-section of the filter header cap 504 andfiber bundle showing simulated blood flow lines from the aperture of theheader cap and into the ends of the fibers. The blood flows in straightflow lines 547 from the aperture and into the center zone 575 of the endsection of the fiber stem, as shown by flow lines 540. Flow stream lines548 show the blood turning in laminar flow around the corner 507 andinto the narrow depth of the annular flow zone 574. As the flow 549spreads out into the annular flow zone, the blood flows into the ends ofthe fibers at the end surface 505 of the stem. Dead zones of blood flowdo not appear in the stream lines shown in FIG. 9.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiment, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

1. A filter for an extracorporeal blood circuit comprising: a bundle ofhollow fibers having an end section encased in a potting material,wherein said end section further comprises a stem of fibers and pottingmaterial and an annular disk of the potting material extending radiallyoutward from the stem, wherein the annular disk of the potting materialis substantially wider than the stem, the stem protrudes from the diskand the stem includes a side surface extending along a length of thestem; an end surface of the stem substantially perpendicular to thelength of the stem and including open ends of the fibers distributedthroughout the end surface including open ends proximate to a perimeterof the end surface; a filter housing through which extends said bundle,said filter housing comprising a tubular section and a first end sectionand a second end section at opposite ends of the tubular section,wherein the annular disk is seated in the first end section and the stemis narrower than the tubular section along the length of the stem; afilter header cap mounted on the first end section of the filterhousing, wherein the filter header cap includes an inlet connectable toa blood line and an open end, said filter header cap including a capside surface abutting the stem side surface, and the second end sectionconnectable to a blood line.
 2. The filter of claim 1 wherein the bundleof fibers has a diameter in the stem substantially the same diameter asthe bundle of fibers in the filter housing.
 3. The filter of claim 1wherein the bundle of fibers has a substantially constant diameterthrough the stem, disk and filter housing.
 4. The filter of claim 1wherein an annular flow zone is formed between an inside surface of thefilter header cap and the end surface of the stem, and a ratio of adiameter of the stem to a maximum depth of the annular flow zone is nogreater than 1 to
 10. 5. The filter of claim 1 and wherein at least oneof the cap side surface and stem side surface is tapered.
 6. The filterof claim 1 wherein the first end section includes a filter housing caphaving an interior surface to receive the disk and an exterior surfaceto receive the filter head cap.
 7. The filter of claim 6 wherein afiltrate chamber is defined between the bundle, filter housing cap andthe disk.
 8. The filter of claim 1 wherein the annular disk issubstantially devoid of the fibers.
 9. The filter as in claim 1 whereinthe end surface includes a rim area of potting material, wherein the rimarea is devoid of the open ends of the fibers and the rim has a width nogreater on average than 0.508 mm.
 10. The filter as in claim 1 wherein adiameter of the end surface is no greater than four times an internalpassage diameter of the blood line.
 11. A filter for an extracorporealblood circuit comprising: a bundle of hollow fibers having an endsection encased in a potting material, wherein said end section furthercomprises a stem of fibers and potting material extending from a disk ofthe potting material, wherein the stem of fibers and potting materialhas an outside diameter of the stem substantially narrower than anoutside diameter of the disk of potting material, an end surface of thestem includes open ends of the fibers distributed throughout the endsurface including open ends proximate to a perimeter of the end surface,the stem including a stem side surface transverse to the end surface ofthe stem; a filter housing through which extends said bundle, wherein aninside diameter of the housing is substantially greater than an outsidediameter of the stem; a filter housing cap at a first end of the filterhousing, wherein an interior annular surface of the filter housing capabuts an exterior annular surface of the disk; a filter header capincluding an inlet connectable to a blood line and an open end, saidfilter header cap including a cap side surface substantially parallel tothe stem side surface, said cap side surface abuts the stem sidesurface, and at least one of the cap side surface and stem side surfaceis tapered along the abutment, and the filter housing including a secondend having an outlet connectable to a blood line.
 12. The filter ofclaim 11 wherein the bundle of fibers has a diameter in the stemsubstantially the same diameter as the bundle of fibers in the filterhousing.
 13. The filter of claim 11 wherein the bundle of fibers have asubstantially constant diameter through the stem, disk and filterhousing.
 14. The filter of claim 11 wherein the stem forms a postextending from the disk, and the disk includes an annular ring ofpotting material devoid of fibers and extending radially outward fromthe stem and the bundle of fibers.
 15. The filter of claim 11 wherein anannular flow zone is formed between an inside surface of the filterheader cap and the end surface of the stem, and a ratio of a diameter ofthe stem to a maximum depth of the annular flow zone is no greater than1 to
 10. 16. The filter as in claim 11 wherein the end surface includesa rim area of potting material, wherein the rim area is devoid of theopen ends of the fibers and the rim has a width no greater on averagethan 0.508 mm.
 17. The filter as in claim 11 wherein the end surfaceincludes a rim of potting material devoid of the open ends of the fibersand the rim has an average width in a range of 0.025 mm to 0.508 mm. 18.The filter as in claim 11 wherein a diameter of the end surface is nogreater than four times an internal passage diameter of the blood line.